This invention relates to peroxide/unsubstituted or alkyl substituted benzoic acid compositions and methods of using these compositions in polymerization and crosslinking; more particularly, this invention relates to compositions of dry solid free-flowing peroxides having melting points greater than 30.degree. C., benzoic acid or alkyl substituted benzoic acids with melting points above 40.degree. C. and optionally a dust suppressant.
This invention also comprehends processes for polymerizing ethylenically unsaturated monomers by polymerizing said monomers in the presence of an initiating amount of the above mentioned solid peroxide composition and for curing of unsaturated polyester resins and diethylene glycol bis(allyl carbonate) monomer by crosslinking in the presence of an initiating amount of the above mentioned solid peroxide composition.
Many peroxide compositions are described in the prior art, although none of them teaches the instant invention. U.S. Pat. No. 3,538,011 describes solid, free-flowing stabilized compositions containing organic peroxides and organic fillers and the methods for the production of these compositions. Organic peroxides employed in this patent for these organic peroxide/organic filler compositions are aromatic and aliphatic diacyl peroxides, ketone peroxides and peroxyesters that are solid at room temperature whereas, the organic fillers employed are solid plasticizers that are soluble in polyester resin masses and are solid at room temperature, such as dicyclohexyl phthalate (m.p. 63.degree.-5.degree. C.). These organic fillers are claimed to reduce the explosiveness and the shock sensitivity of the organic peroxides employed. Nevertheless, these formulations with dibenzoyl peroxide were found to be thermally unstable stored at 70.degree. C. relatively short time periods (see Example X, infra).
U.S. Pat. Nos. 2,453,070 and 2,453,071 disclose impact shock desensitized dibenzoyl peroxide compositions in which the preferred compositions are desensitized with 2 to 10% aliphatic carboxylic acids such as lauric acid and less preferably desensitized with 5% phthalic acid and 5% salicylic acid. 50% Dibenzoyl peroxide compositions containing aliphatic carboxylic acids such as lauric acid or other acids such as phthalic acid or salicylic acid were found to be more hazardous in burning (see Example XV, infra) and were significantly less thermally stable (see Example XVII, infra) than was an invention 50% dibenzoyl peroxide composition containing benzoic acid. In addition, this invention composition was significantly more active in curing of an unsaturated polyester resin composition than were comparable 50% dibenzoyl peroxide compositions containing salicylic acid or phthalic acid (see Example XVI, infra).
The prior art also is repleted with many peroxide paste compositions containing one or more organic safety liquids and water. Although these peroxide pastes and suspensions are described to be safe, none of them teach the safe, free-flowing solid peroxide/unsubstituted or alkyl substituted benzoic acid composition of the present invention that have been found to be significantly more permanently stable than similar prior art formulations and considerably more resistent to burning ignition. Moreover, the benzoic acid as a filler in the instant invention has no detrimental effects on the rate of solution of, or the polymerization or curing efficiency of the formulation in ethylenically unsaturated monomers, such as styrene or in unsaturated polyester resins.